How FM Synthesis Really Works with OP-1 and OP-1 Fields

In a recent article, we posed the question “Does hardware still shape genres”? To continue on the theme, it’s been ten years since Teenage Engineering released the OP-1. Now discontinued but with its spiritual successor, the OP-1 field, perhaps its legacy needs to be revisited. Since the OP-1’s debut, we’ve seen a positive tsunami of small, ultra-portable FM machines. Was it the trigger for a new generation of FM musicians addicted to FM sound? If that’s the sound you need, in this Hardware Focus we show you how to use the OP-1 for powerful FM synthesis.

Appearing at the end of the 1970s, FM (frequency modulation) synthesis quickly became the essential reference in the studio, and it remained so until the end of the 1980s. Although it is known for its methodology of unfathomable programming, FM synthesis has never lost its appeal. Thirty years later, Teenage Engineering released the OP-1. After only ten years, it was abandoned and its spiritual successor, the OP-1 Field, put in place. Looking back, has Teenage Engineering released the ultimate FM hero?

Before digging, a bit of history. Through the subsequent overuse of a number of presets, FM’s unique sonic signature (a technological blend of glassy, ​​fragile highs, punchy mids, and surprisingly deep pads and washes) faded away until the late 2000s when new FM hardware and software began to hit the market, a collective attempt to right the wrongs of the past and make FM accessible and relevant for today.

It’s not often discussed as such, but one of the earliest representatives of this FM legacy redux was the much loved/hated OP-1. And now his successor, the Field OP-1take over.

Brimming with deliberate contrarianism, the quirky little white box offered FM among its roster of 11 synth engines at a time when virtual analog was the flavor of the month.

Indeed, the FM engine was the first to be developed, (source code indicating ©2009) the reason being, as Teenage Engineering co-founder David Möllerstedt puts it‚ “it seemed logical to present a type of synthesis entirely digital on a resolutely digital machine.

It’s hard to prove but my theory is that through the success of dedicated FM users (I’m thinking of Stuart Price, shameless DX7 enthusiast (Les Rhythm Digitales, Zoot Woman) as an example), the distinctive sound began to trickle down to independent music in the late 1990s, arguably emerging with its own genre in synthwave.

With such a market to tap into, it’s no surprise that a leftist music tech company like TE is making new hardware FM instruments. Additionally, the positive tsunami of small, ultra-portable FM machines released since that time suggests that the OP-1 has had some influence beyond just sound production. The sheer availability of FM today has inevitably drawn a new generation of musicians to the FM sound – perhaps one reason why we hear its influence all over “pop” music today.

it seemed logical to present a fully digital type synthesis on a resolutely digital machine.


The foundation of FM on the OP-1 rig is its four-operator* system, small self-contained synthesizer units that are connected either to other operators or directly to the output, with routing adjustable by nine configurations or algorithms**, which together cover the fundamental FM timbres – piano, strings, organ, percussion, bass, synth pads and, if you wish, some rather pleasant abstract noises.

For those unfamiliar with the OP-1 UX, the FM engine is launched by pressing the synth button on the far left of the device’s front panel. The buttons marked 1 through 8 (in small print), to the right of the buttons marked 1 through 4 (in large print) are the 8 slots available for synth patches which, on a unit fresh from the factory, are already loaded.

By pressing one of the buttons marked from 1 to 8, simultaneously with the Shift button, you access the menu of the synthesis engine. Turning the blue knob toggles the synth engines and enables FM selection. Turning the beige knob toggles the available presets, a comprehensive overview of the OP-1’s FM capabilities but, if we were to be critical, they’re all one type. As with many machines throughout its history, the FM is capable of much more than the presets suggest, and so it is here.


Given its trademark user interface, it would be easy to think that the field maps one operator per encoder, but the procedures are a bit more involved than that. When you start creating a new sound, the OLED display provides the only interpretation.

The FM engine is visually represented by four isometric wireframe cubes, one being B, for base frequency, and the rest showing fractions or decimals that represent all other operator frequencies, or not relative, being either a ratio (1/2, 1/4, 3/8, etc.) or a multiple (2, 3.5, 4, etc.) of this base frequency. These alphanumerics are displayed in a color corresponding to one of the encoders.


Blue encoder = FM intensity

Blue controls the level of each of the non-Base operators, i.e. modulation depth if an operator is a modulator or volume if the operator is a carrier. The levels are represented on the OLED by progressively brighter blue outlines around the cubes. Setting the CCW encoder to its minimum value will bring the level of all other non-Base operators to 0, regardless of where their encoders are pointing.

At this point you will hear something very similar to a pure sine tone. This is the base frequency which, using the “snapshot” feature, can be saved as an approximation of what other instruments would call an “init” patch to use as the basis for new sounds.

Turning CW blue, the depth of modulation increases, introducing higher frequencies and rounding out the sound by increasing intensity and sharpness. At the maximum CW setting, an aggressive, noisy tone is produced, although the overall flavor will vary depending on the values ​​of the other parameters.

Beige encoder = frequency

The Beige command determines the relative frequencies of each operator, which it does by presenting “sets” that each define three values: the frequencies of the green, white, and orange operators, each relative to the base frequency.

Starting from the minimum CCW setting and rotating clockwise, the green operator frequency increases, covering 8 different values: 1/64, 3/32, 1/8, 5/16, 1/2, 5/ 8, 1 and 2. For each of these green frequencies, the white operator has its own range of 8 frequencies, which decrease with the movement of the encoder: 2, 1.5, 1, 1/2, 3/4 , 1/4, 5/32, & 1/32. Finally, for each white value, there are 8 other frequencies for the orange operator which appear as a more random sequence: 1/16, 2, 5/8, 4 , 1.75, 7/16, 3.5 and 1

Each movement of the encoder registers a change in the orange frequency while the white operator changes after orange has run through its range for the particular value associated with white. Similarly, the green operator changes after white has run its range for each value of green.

Although there is clearly a numerical pattern in the sets of frequencies, this does not translate into a particular timbre. The sound varies enormously, from harmonic to discordant, even between adjacent values.

If you like FM synthesis and electronic music in general, come to Attack Live in London on September 29th.

Gray encoder = topology

The gray button controls the algorithm selection. On the OLED display, the arrangement of the cubes indicates their current function. Operators that do not have a neighbor below or to the side are carriers or “exit” operators, which produce the audible sound due to their frequencies above the audio rate. The operators in the middle of the graph are modulators or carriers.

A useful starting point is to note that in the extreme CCW setting, all cubes appear diagonally adjacent in left-to-right order. The operators are now in serial configuration (orange>white>green>B), the top left cube being the modulator, bottom right the carrier.

The parallel CW configuration arranges adjacent cubes diagonally from right to left (B > green > white > orange). Here the carriers and modulators are mixed and the four operators are sent directly to the output without modulation. In both configurations, the sound is practically identical.

The volume of the Base operator will vary depending on the topology; when there is more than one “output” operator, the level of B is reduced. This is evident when Blue is turned fully counterclockwise and the motor generates a pure sine tone. Only when the FM color is increased to about 10 notches will any noticeable change in sound color be heard when changing the algorithm.

Orange encoder = disagree

This last parameter is the most obvious and can be used to create extreme inharmonic sounds or to introduce motion. Visually, the amount of Detune is indicated by the B and the white cube being increasingly shifted to the right, the latter more than the former, while the green and orange cube are shifted to the left where, again, the latter has a greater momentum than the former.


The field differs from earlier and later incarnations of FM in its provision of
pre-determined sets of frequencies. It is therefore absolutely not a “free” function generator. That said, even with 2 operators less than the unofficial industry standard of 6 and its 9 algorithms, the final conclusion cannot be to say that the field is lacking.

It is well documented that this was a deliberate design decision on the part of teenage engineers to create in the OG, and now the field, an instrument with built-in limitations, a utopian move that aimed only to unlock the inherent properties of its users. creativity.

Brimming with deliberate contrarianism, the quirky little white box offered FM among its roster of 11 synth engines at a time when virtual analog was the flavor of the month.

The FM Engine probably exemplifies this intent more fully than any of the other synth designs available. The successful innovation of the OP-1, which arguably inspired every machine that followed it, was to demonstrate that by creating a feature deficit, it is possible, by paying close attention to UX detail, to credit the user with a huge “pick up and play”. ‘ assess.

In pure FM terms, through the Field and OG the user is freed from the double-edged sword that is this synthesis mode, namely the risk of being bogged down by too many possibilities or finding what it takes for a doctorate in acoustics. before you can make a sound.

Buy the OP-1 field here and the original OP-1 here.

While you are here:

If you like FM synthesis, you might enjoy Attack Live! It’s free, in London on September 29. Subscribe to the guestlist by filling out the form below.

‘Attack Live’ is Attack’s first live event dedicated to live electronic music

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Author Jeremy Owen
September 17, 2022

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